1. Field of the Invention
The present invention relates to a robot teaching machine that uses a dummy tool operated by an operator so as to guide a robot to a precise working position on a workpiece.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. Hei 8-8221 (Application date: Jan. 22, 1996) discloses a robot teaching machine, which has been filed by the same applicant of the present invention.
As shown in FIG. 1, the above-identified robot teaching machine is provided with a teaching pen 10 having a dummy tool T fitted therein. The dummy tool T has the same shape as that of the tool used for actual working operations. An operator takes a grip of the teaching pen 10 by one hand and also a teaching pendant 81 by the other hand to bring the dummy tool T into a desired guiding position on a workpiece W. The operator, then, depresses a guiding button 82 on the teaching pendant 81. In response to depression of the guiding button 82, a position defined as a three-dimensional coordinate and an attitude (inclined amount) of the teaching pen 10 are stored as guiding data.
The position of the teaching pen 10 defined as the three-dimensional coordinate is detected by a teaching compass 30 that is connected with the teaching pen 10 via a wire 60 and follows the three-dimensional movement of the teaching pen 10.
The teaching compass 30 detects a distance between the teaching pen 10 and the teaching compass 30 based on a two-dimensional position of the wire 60 and an amount of rotation of a take-up reel provided with the teaching compass 30 at a time when the wire 60 is supplied therefrom. The three-dimensional coordinate position of the teaching pen 10 is detected in the aforementioned manner.
The wire 60 that connects the teaching pen 10 with the teaching compass 30 is constantly kept under tension by a force generated by the take-up reel such that the movement of the teaching pen 10 is precisely transferred to the teaching compass 30. Such tensile force applied to the wire 60 allows the teaching compass 30 to follow the movement of the teaching pen 10 precisely.
The conventional robot teaching machine uses only the wire 60 as a motion transfer member connecting the teaching pen 10 with the teaching compass 30 for following the three-dimensional movement of the teaching pen 10. The above construction often prevents the teaching compass 30 from following the movement of the teaching pen 10 precisely because of the friction generated between bearings that support the respective rotating portions of the teaching compass 30. A winding force of the take-up reel may be increased to improve the following capability of the teaching compass 30. In this case, however, the teaching pen 10 is likely to become unnecessarily inclined during guiding operations, thus requiring additional time period for corrective operations.